Composite bonding resins can fracture. Unhappily, sometimes it is yesterday's bonding. But some bonding resins placed in the mouth 7, 10 or 14 years ago, though not always color stable, are still intact. This mystery has traditionally been answered by focusing on case selection; the resins have fared far better in low-stress areas. Resins placed in areas which overstress their tensile abilities will fail. Those of us who style smiles and are continually attempting to lengthen, widen and rotate teeth with composite materials have faced artistic and technical limitations. Cantilevering composites has been an anathema. Since these filled resins have no continuous internal matrices, they absorb stress almost entirely at the points of impact. Hence the more your composite resin hangs off the side of the tooth, the more the practitioner is out on a limb. If the patient is additionally a bruxer, the restoration will fail.
Buonocare, Jordan, Gwinnett, Pollack and others have described the properties and limitations of microfills, macrofills and hybrid bis-GMA resins. Clinicians have devised techniques to minimize the fracture of cantilevered composite resin, including, (1) over-relieving interferences in protrusive and lateral excursions, (2) rounding sharp line angles of the enamel structure, (3) utilizing as much enamel surface as possible for adhesion, (4) roughening the tooth surface with abrasive diamond stones before etching (Goldstein, Black), (5) insuring that the etchant and bonding adhesive is wrapped into the interproximal areas (Hendell), (6) using macrofills for the majority of the buildup and microfills only for the final outer surface. Still, bonding has had its limitations. Teeth which have needed to be lengthened or widened considerably, such as openbite cases or malformed, retruded or malposed teeth (and of course missing teeth) have always required conventional crowns and conventioal bridges. Even Maryland Bridges have necessitated some form of metallic frame, and therefore, laboratory intervention.